Invalidate cache upon file deletion

If a file stored in the cache is deleted, it should automatically be
removed from the cache without requiring manual invalidation.
Merge pull request #451 from keelerm84/feature/remove-from-cache

Invalidate cache upon file deletion
Merge pull request #452 from tuhdo/master

Remove another unnecessary action and update README
Merge pull request #455 from tuhdo/master

Update key binding description